Corrosion inhibition with propargyl cyclohexylamine



United States Patent O This invention relates to the inhibition of metal corrosion in acidic solutions and is more particularly concerned with inhibited aqueous acid solutions suitable for the treatment of metals.

Metal cleaning baths and pickling baths generally comprise aqueous solutions of inorganic acids such as sulfuric acid, hydrochloric acid, and phosphoric acid and are useful in the cleaning and treatment of iron, zinc, ferrous alloys and the like.

In the use of aqueous acidic baths to treat metals, additives or inhibitors in the baths are desirable to prevent or inhibit corrosion or erosion of the metal surfaces. If no corrosion inhibitor is present in the acidic bath, excessive metal loss, production of undesirable metal surface properties, excessive consumption or less of acid, and like adverse results will be experienced. While it is Well-known to use corrosion inhibitors in such acidic baths, and many different types of inhibitors have been proposed, there has been a continuing search for inhibitors which can be effectively used even in very low concentrations.

It is accordingly an object of this invention to provide an improved means for the protection of metal surfaces against erosion or corrosion in aqueous acid solutions.

Another object of this invention is to provide a novel inhibited aqueous acidic composition.

A further object of the invention is to provide improved metal treating baths containing an inhibitor which is effective to inhibit corrosion even when present in very low concentrations.

These and other objects are achieved in accordance with the present invention by the incorporation in aqueous inorganic acid solutions of a small but effective inhibiting amount of propargyl cyclohexylamine, which has the formula C H E Propargyl cyclohexylamine is readily prepared by interacting propargyl bromide of the formula BrCH CECH, and cyclohexylamine, e.g. by the procedure described by von Braun et al. in Berichte der Deutschen Chemischen Gesellschaft, vol. 59 (1926) pp. 10814090, or the procedure described by Wolf in Annalen der Chemie, vol. 576 (1952) pp. 3545.

The introduction of propargyl cyclohexylamine in aqueous inorganic acid solutions has been found to have the desirable result of inhibiting or substantially preventing the corrosive action or attack of the acid upon metal surfaces with which it comes into contact. The use of propargyl cyclohexylamine in acid cleaning and pickling baths does not hinder or interfere with the desired action of the acid on the oxide, rust, grease, scale, or other undesirable surface material or coating which is to be re moved.

The inhibitor of this invention is useful, in general, in the inhibition of corrosion of metal surfaces in contact with aqueous mineral acid solutions, for example, in the acidizing of oil wells, electrolytic cleaning baths, and electrolytic refining of metals, as Well as in metal cleaning and pickling baths.

The use of propargyl cyclohexylamine as a corrosion inhibitor for metals in aqueous mineral acid solutions is advantageous in that propargyl cyclohexylamine can be employed as a corrosion inhibitor over a wide and useful concentration range. A further advantage of this inhibitor is that it may be used even at elevated temperatures to provide good corrosion inhibition, even when in low concentration.

The most effective amount of propargyl cyclohexylamine to be used in accordance with this invention can vary, depending upon local operating conditions. Thus, the temperature and other characteristics of the acid corrosive system may have a bearing upon the amount of inhibitor to be used.

In general, it has been found that a concentration of propargyl cyclohexylamine between 0.01% to 0.5% by weight of the aqueous acidic solution is an effective corrosion inhibiting concentration, with a concentration between 0.05% ao 0.5 being particularly preferred, especially for corrosive systems at elevated temperatures, e.g. in the neighborhood of C. The acidic solution can be dilute or concentrated and can be of any of the concentrations used in treating metals, e.g. ferrous metals, for example 5 to 80% The following specific examples are illustrative of the corrosion inhibiting properties of propargyl cyclohexylamine. In the examples,the inhibitor concentration is expressed as a percent by weight of the aqueous acidic solution in which it is incorporated and the acid concentration of the solution is expressed as percent by Weight of the solution. The method used to determine the inhibiting properties of propargyl cyclohexylamine as set forth in the following examples, employed test specimens of low carbon 1020 steel. Coupons in. x 1% in. were cut from the steel sheet-stock and pickled in dilute HCl to remove scale and surface film. After pickling they were dipped in sodium bicarbonate solution, rinsed well in tap water while rubbing with a piece-of cotton, rinsed in distilled water and finally dried with acetone. The clean and dry specimens were thenweighed to the nearest 0.1 mg., all handling being effected with forceps to keep the coupons free of oil or moisture from the hands. The propargyl cyclohexylamine was Weighed and placed in ml. of the acidic solution. Weighed and identified coupons in duplicate were supported on glass hooks in a 4 oz. glass jar, the solution being studied added, the jar covered and placed in a constant temperature oven at 80 C. for 3 hours. At the end of the exposure period, the jars were removed from the oven, samples removed, rinsed with tap water, sodium bicarbonate solution, tap water, distilled water and finally acetone. The dry coupons were weighed and the percent inhibition calculated by subtracting the loss in weight of the coupon from the original weight, dividing 'by the original weight and multiplying by 100. This is expressed by the following formula:

Percent inhibition= (original weight specimen-weight loss) X 100 original weight specimen The results are expressed as percent inhibition and are the average of the duplicate samples.

The following examples illustrate the corrosion inhibiting properties of propargyl cyclohexylamine:

Example 1 Using the procedures described above, steel coupons cut from low-carbon 1020 steel of 16 gauge were immersed in 4.8 N hydrochloric acid containing varying concentrations of propargyl cyclohexylamine at 80 C.

3 (176 'F.) for 3 hours. The following results were obtained:

Inhibitor concentration, Immersion corrosion percent: rate, percent: 0.1 99+ 0.5 99+ None (control) 53 Example 2 Inhibitor concentration, Immersion corrosion percent: rate, percent: .05 98 None (control) 6 Example 3 Using the procedures described above, steel coupons were immersed in a solution of 4.8 N sulfuric acid at a temperature of 80 C. (175 F.). The inhibitor concentrations were those employed in Example 1. The results are tabulated below:

Inhibitor concentration, Immersion corrosion percent: rate, percent: 0.1 98 0.5 97 None (control) 61 Example 4 In order to demonstrate further the outstanding effectiveness of propargyl cyclohexylamine in sulfuric acid, coupons cut from the steel used in Example 2 were immersed Inhibitor concentration, Immersion corrosion percent: rate, percent: .05 97 None (control) 14 It will be understood that various changes and modifications may be made in the foregoing description without parting from the scope of the invention, as defined in the appended claims and it is intended, therefore, that all matter contained in the foregoing description shall be interpreted as illustrative only and not as limitative of the invention.

We claim:

1. A method of inhibiting the corrosion of metals by an aqueous solution of a mineral acid which comprises incorporating in said solution an effective corrosion inhibiting amount of propargyl cyclohexylamine while said solution is in contact with said metal.

2. A method of inhibiting the corrosion of metals by an aqueous solution of a mineral acid which comprises incorporating in said solution 0.01 to 0.5% by weight of the solution of propargyl cyclohexylamine while said solution is in contact with said metal.

References Cited UNITED STATES PATENTS 2,766,285 10/ 1956 Hennion 260563 3,007,933 11/1961 Hennion 26O563 XR 3,113,113 12/1963 Marsh et al 252-148 XR OTHER REFERENCES Foster et a1.: Acetylenic Corrosion Inhibitors Industrial and Engineering Chemistry (July 1959), pp. 825-828.

LEON D. ROSDOL, Primary Examiner.

W. E. SCI-LULZ, Assistant Examiner. 

1. A METHOD OF INHIBITING THE CORROSION OF METALS BY AN AQUEOUS SOLUTION OF A MINERAL ACID WHICH COMPRISES INCORPORATING IN SAID SOLUTION AN EFFECTIVE CORROSION INHIBITING AMOUNT OF PROPARGYL CYCLOHEXYLAMINE WHILE SAID SOLUTION IS IN CONTACT WITH SAID METAL. 